EGG VOLUME AND WITHIN-CLUTCH ASYMMETRY IN GREAT SKUAS - ARE THEY RELATED TO ADULT QUALITY

In gulls, egg size and clutch asymmetry have been suggested to be suit able variables for assessing individual quality. Skuas, like several o ther seabirds, generally display within-clutch asymmetry (the second e gg in the clutch is, on average, smaller than the first egg). We found no relationship between clutch volume in 2-egg clutches and laying da te, hatching success or fledging production of pairs of Great Skuas (C atharacta skua) breeding in Shetland. There was a high repeatability ( 0.72, P < 0.0001) in the volume of clutches laid by the same pairs in consecutive years. The influence of adult age on egg size was weak and variable. Unlike clutch volume, clutch asymmetry was not repeatable a nd showed no relationship with adult age. Futhermore, clutch asymmetry did not correlate with any other breeding parameter. We conclude that , in Great Skuas, clutch characteristics are not suitable indicators o f individual quality or environmental conditions over the range prevai ling during this study. The results are discussed in comparison with t he conclusions from studies with gulls, and it is argued that more res earch is needed to clarify the factors that are responsible for the ex istence of within-clutch asymmetry in seabirds.